Flying club a few questions

Ok perhaps someone who has used their Flying Club for flights can help. I know I can upgrade from economy to PE with mile but does that mean I can then also gte a friend a PE ticket on a companion flight or does my flight have to be PE to start with? If my flight has to be PE to start with which fare codes are applicable to the companion ticket?

You have to pay full fare PE to get the Companion flight. And there are a limited number of reward fares in each class. We managed to get two free PE flights to DC using miles, but when our friends then immediately tried to book their Companion flight, they couldn't get it because we'd used the entire availability for that flight in that class. We'd phoned separately to confirm availability, but it didn't occur to us to ask how many fares were available.